This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2005-252123 filed in Japan on Aug. 31, 2005, the entire contents of which are hereby incorporated by reference.
The present invention relates to an optical transmission connector for use in an electronic apparatus, such as a DVD player, a DVD recorder, a liquid crystal TV, a Set Top Box (STB: an adaptor apparatus for satellite broadcast), an AV receiver, or the like, and an electronic apparatus employing the optical transmission connector.
An optical transmission connector which transmits an electrical signal as an optical signal has been proposed. The optical transmission connector is constructed as an optical fiber link which employs an optical fiber, and is becoming adopted, as a transmission system which can reliably eliminate noise caused by an electrical signal, in a DVD player, a DVD recorder, a liquid crystal TV, an STB, an AV receiver, and the like which require a high level of noise withstanding capability.
The optical transmission connector is conventionally fixed to mounting boards of these electronic apparatuses with screws. However, from the viewpoint of workability and outer appearance, there has been a demand for an optical transmission connector of a self-standing type which is directly attached to a mounting board.
An optical transmission connector which functions as a transmitter unit or a receiver unit, comprises an element housing unit (a light emitting element unit or a light receiving element unit) for housing a photoelectric effect element (a light emitting element or a light receiving element), a holder unit comprising an optical plug housing unit for housing an optical plug which is composed of a fiber-optic cable and is used for transmission of an optical signal, a shutter mechanism for opening and closing the optical plug housing unit, a spring (coil spring) for biasing a shutter plate of the shutter mechanism in a direction in which the shutter plate is closed, and a fixing metal plate for mounting and fixing the holder unit to a mounting board.
This optical transmission connector is provided with the shutter mechanism which prevents dust and foreign matter from entering the element housing unit and the plug housing unit, and protects eyes from leakage light. The shutter mechanism is configured to open or close a lid (shutter plate), depending on insertion or extraction of an optical plug.
FIG. 8 is a front view of a conventional optical transmission connector as viewed from a side from which an optical plug is inserted.
A conventional optical transmission connector 101 comprises a shutter mechanism unit 105 which serves as an insertion opening through which an optical plug (not shown) is inserted into a front portion of a holder unit 102. A lead terminal 107 of a photoelectric effect element (not shown) housed in the holder unit 102, and a fixing terminal unit 108t of a fixing metal plate 108 (see FIGS. 9A and 9B) for mounting and fixing the holder unit 102 to a mounting board 140 (see FIGS. 9A and 9B), are each protruded from a bottom surface of the holder unit 102. A hemispherical protrusion 108b for fastening the holder unit 102 to the mounting board 140 is formed on the fixing terminal unit 108t. 
FIGS. 9A and 9B are diagrams for explaining an action of the fixing metal plate of the conventional optical transmission connector. FIG. 9A is a partially cross-sectional, front view as viewed from a side from which an optical plug is inserted. FIG. 9B is a left side view thereof. Note that FIG. 9A indicates a cross-section of the mounting board 140, taken at a position corresponding to a fitting hole 140h, and FIG. 9B indicates a cross-section of the mounting board 140, taken along line B-B of FIG. 9A.
When the optical transmission connector 101 is mounted on the mounting board 140, the fixing terminal unit 108t formed at a tip of the fixing metal plate 108 for fixing the holder unit 102 to the mounting board 140 is inserted into the fitting hole 140h formed in the mounting board 140, so that the holder unit 102 is fixed to and held on the mounting board 140.
The protrusion 108b formed on the fixing terminal unit 108t is formed at a position which matches a board thickness of the mounting board 140, so that the protrusion 108b butts and engages with the mounting board 140 on a bottom surface 140bs (an opening end portion of the fitting hole 140h) of the mounting board 140. However, the protrusion 108b has a hemispherical shape, and therefore, the butt and engagement are only achieved at a point on the great circle (having the maximum diameter) of the hemisphere. Therefore, when external force is applied to the holder unit 102, the fixing terminal unit 108t can be moved and swayed along a hemispherical line, depending on the external force. In other words, the protrusion 108b (the fixing terminal unit 108t) for fixing and stabilizing the holder unit 102 does not achieve the desired purpose, so that the optical transmission connector cannot be stably connected to an optical plug (not shown).
FIG. 10 is an exploded side view for explaining how the conventional optical transmission connector is assembled.
The holder unit 102 included in the conventional optical transmission connector 101 has two separate units, i.e., a front housing unit 102f and a rear housing unit 102r. 
The front housing unit 102f and the rear housing unit 102r are joined together to assemble the optical transmission connector 101 in accordance with the following procedure.
Initially, the shutter mechanism unit 105 including a shutter plate 110 is attached to the front housing unit 102f from the inside thereof. A coil spring 113 is engaged and incorporated with a coil spring holding post 117 provided in the rear housing unit 102r. 
Next, the front housing unit 102f is fitted into the rear housing unit 102r in a direction indicated with arrow A to be mutually joined with the rear housing unit 102r. Thereafter, the fixing metal plate 108 is fastened to a metal plate fastening concave portion 102p formed on a surface of the rear housing unit 102r in a direction indicated with arrow B to be mutually joined with the metal plate fastening concave portion 102p. Further, a holder cover (not shown) is attached to surfaces of the rear housing unit 102r and the fixing metal plate 108, thereby obtaining a complete structure of the optical transmission connector 101.
Note that a fastening hole 102h for fastening a nail portion 108p provided on the fixing metal plate 108 is formed in the rear housing unit 102r. By fitting the nail portion 108p into the fastening hole 102h, the fixing metal plate 108 is fixed to the rear housing unit 102r so as to secure mechanical strength.
The conventional optical transmission connector 101 thus constructed has a complicated assembly structure and a large number of parts, resulting in high manufacturing cost.
The coil spring 113 is fixed to the rear housing unit 102r only by pressure applied by the front housing unit 102f after the coil spring 113 is incorporated into the rear housing unit 102r. Therefore, for example, the coil spring 113 is likely to be detached from the rear housing unit 102r, i.e., there is a problem with reliability. In addition, the assembly process is complicated, resulting in an increase in cost.
When the optical transmission connector 101 is mounted on the mounting board 140, a flux for soldering is used. The flux seeps up through a gap between the front housing unit 102f and the rear housing unit 102r, leading to an interference with opening/closing of the shutter plate 110.
When the nail portion 108p of the fixing metal plate 108 is fitted into the fastening hole 102h of the rear housing unit 102r, the fitting work is not easy, resulting in low workability.
Note that there is also a known conventional optical transmission connector which is disclosed in JP 2000-131564A.